Research And Design Of Process For Treating Sweet Potato Starch Waste Water

This paper describes the reason of causing sweet potato starch wastewater fromfactories. The wastewater is mainly produced in the grinding process and separatingprocess. The values of its COD and BOD5are very high. It is high concentrationsorganic wastewater. If it is discharged without treating, the water in the nature will beseriously polluted by the wastewater. Environmental factors severely limit the starchindustry. The design of an effective wastewater treatment system for sweet potatostarch industry has important significance.Because the pollution indexes of sweet potato starch waste water are very high,neither ordinary physical nor chemical treating methods are effective. Sweet potatostarch wastewater mainly contains soluble sugars, starch, cellulose, protein and othernatural organic ingredients, and does not contain toxic substances. Biological treatingmethods which are usually used to treat high concentration organic wastewater arefeasible to the sweet potato starch wastewater. This design mainly uses anaerobicbiological treating methods. UASB and CAST reactors are chose to treat the wastewater. After the treatment of UASB, the COD of wastewater is highly reduced.However, it still can’t be permitted to discharge. The CAST can’t treat high CODwastewater, but it can make the water fit the standard of discharging. So using bothUASB and CAST may get effective result.The author carried out some relevant simulation experiments by using theprepared sweet potato starch wastewater. The results of the experiments indicate that,the best dosage of PAC is300mg/L, and using lime to adjust pH of wastewater isfeasible. The best Hydraulic Retention Time is18hours, which is confirmed by thelong-term experiments of using a small acrylic UASB model. The removal rate ofCOD by UASB can reach90%.According to the results, this paper designs a large-scale wastewater treatingsystem for sweet potato starch factories. The wastewater flux is10000m3/d, COD= 10000mg/L, BOD5=5000mg/L, SS=3000mg/L. The wastewater is pre-treated bythe grille and grit chamber to remove the large floating debris, sands, etc. which maydamage subsequent processing equipment. Then the inorganic polymer flocculatingagent PAC is added into the wastewater. After mixing equably, lime is added into thewastewater to adjust pH to neutral. Then the wastewater is transported into thesedimentation basin. Vertical flow sedimentation tank is chose to save area. Itstreating effect is better than other styles. After sedimentation, the wastewater passes tothe UASB reactor for anaerobic digestion. The UASB reactor is not made bytraditional reinforced concrete structure but Lipp cans, which can significantly shortenthe construction term and save construction cost. The service life of the UASB is notaffected. Treated by the UASB reactor, the wastewater’s COD can be reduced to1000mg/L. Then, the wastewater is treated by the CAST, which is an improvementmethod of the traditional activated sludge process. It can eliminate the need forsecondary settling tank, reduce the area effectively, and the control of CAST issimpler. Sludge bulking is not easy to occur in this system. After the treatment, wastewater can achieve the secondary emission standard of GB8978-1996.The methane generator is added into this design, so that the methane which isproduced by anaerobic digestion can be adequately used. The electricity which isgenerated by methane can be used in the engineering of waste water treatment, andalso can be used in starch production to reduce the cost of manufacture enterprise. Awin-win of environment protection and economic benefits can come true.